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My 95 525's battery keeps dying. I just put in a new battery last week. It happened last winter once it started to get around freezing temperatures every night. Now that it is getting cold it is happening again. The only thing I can think of is that something is drawing power once I turn the car off. I think the cause is that when it gets cold, when I hit the key fob to lock the car it doesn't actually lock the car, but instead continually tries to lock the doors until the battery dies. If anyone has an explanation or possible solution I would appreciate it greatly.

I believe the way to figure this out is to take a digital ammeter to each fuse in your fusebox and see which ones still carry current after you've removed the key from your ignition.

Some fuses group a few components together, so if you find the right circuit, you might have to do something else to identify the precise component responsible for this. However, usually when you've hit the right group, you'll have a hunch as to exactly what is responsible. Fix that, then retest the fuse, and if the problem has gone away then you're done.

This is an interesting problem and the solution should be fairly simple. Would appreciate if someone who has actually done this or has experience with this posts the correct tested method or corroborates what I said earlier if I'm right.

The way to check for battery drain is as follows, get an ammeter, or a DMM that has an ammeter setting.

Remove the backseat bottom and roll down your rear windows so you can access the fusebox without opening the door.
Remove the negative cable.
connect the ammeter between the neg. cable and the negative battery post.
Wait a few seconds for all the electronics and check control to shut down.
There should be a small battery drain that is used for the clock, about less than .03 amps
Anything more than that value....begin by pulling fuses in the front, then rear fusebox while watching the ammeter for a drop in current drawn.
If the current comes down to less than .03 amps you have found the circuit draining the car!
ID and fix circuit accordingly.

The way to check for battery drain is as follows, get an ammeter, or a DMM that has an ammeter setting.

Remove the backseat bottom and roll down your rear windows so you can access the fusebox without opening the door.
Remove the negative cable.
connect the ammeter between the neg. cable and the negative battery post.
Wait a few seconds for all the electronics and check control to shut down.
There should be a small battery drain that is used for the clock, about less than .03 amps
Anything more than that value....begin by pulling fuses in the front, then rear fusebox while watching the ammeter for a drop in current drawn.
If the current comes down to less than .03 amps you have found the circuit draining the car!
ID and fix circuit accordingly.

I have saved this for my personal use should I need it in the future. Very nice succinct and to the point directions

The way to check for battery drain is as follows, get an ammeter, or a DMM that has an ammeter setting.

Remove the backseat bottom and roll down your rear windows so you can access the fusebox without opening the door.
Remove the negative cable.
connect the ammeter between the neg. cable and the negative battery post.
Wait a few seconds for all the electronics and check control to shut down.
There should be a small battery drain that is used for the clock, about less than .03 amps
Anything more than that value....begin by pulling fuses in the front, then rear fusebox while watching the ammeter for a drop in current drawn.
If the current comes down to less than .03 amps you have found the circuit draining the car!
ID and fix circuit accordingly.

Well, in a scenario where there's an obvious battery drain from somewhere, is it necessary to remove the batt's terminal first ? Can one go straight to the fuses, placing both digiamm leads on them (or is it one on the fuse and the other on an earth point?) and see if any read higher current than 0.3a and that should be the problem?

The way to check for battery drain is as follows, get an ammeter, or a DMM that has an ammeter setting.

Remove the backseat bottom and roll down your rear windows so you can access the fusebox without opening the door.
Remove the negative cable.
connect the ammeter between the neg. cable and the negative battery post.
Wait a few seconds for all the electronics and check control to shut down.
There should be a small battery drain that is used for the clock, about less than .03 amps
Anything more than that value....begin by pulling fuses in the front, then rear fusebox while watching the ammeter for a drop in current drawn.
If the current comes down to less than .03 amps you have found the circuit draining the car!
ID and fix circuit accordingly.

The way to check for battery drain is as follows, get an ammeter, or a DMM that has an ammeter setting.

Remove the backseat bottom and roll down your rear windows so you can access the fusebox without opening the door.
Remove the negative cable.
connect the ammeter between the neg. cable and the negative battery post.
Wait a few seconds for all the electronics and check control to shut down.
There should be a small battery drain that is used for the clock, about less than .03 amps
Anything more than that value....begin by pulling fuses in the front, then rear fusebox while watching the ammeter for a drop in current drawn.
If the current comes down to less than .03 amps you have found the circuit draining the car!
ID and fix circuit accordingly.

Well, I can now positively confirm that there is no need to remove a battery terminal and hook up the ammeter in between, and no need* to pull out and replace fuses one by one.

I just tested this on my car. Switched the digital multimeter to the 200ma setting, and place both leads on each exposed end of the top of a fuse you're testing while it still fixed in the fuse box. In this case, I used the luggage compartment or boot. I opened the boot and its internal light came on. The reading was around 13.5 when the car was running and 12.5 when it wasn't. I closed the boot. The reading was zero when the car was running and zero when it wasn't. So that makes sense.

When you identify the fuse that is drawing current, if the description in your fuse box indicates a component that should not be functioning when the engine is off and the key removed, then you've found your current draw. Please check the component's wiring, relays, and/or replace the component itself. If the fuse box's description indicates a group of components, then you'll have to check each component separately for current draw at the component/component's dedicated circuit alone, to isolate the actual culprit.

Please take note that voltage cannot be tested this way. For voltage to be tested, you need to connect one lead to the fuse and the other lead to an earth point, usually a nut on the shock absorber tower for convenience. Of course, the multimeter needs to be switched to 20volts to permit this. Current draw cannot be tested this way....both leads need to be on the fuse itself. My head hurts so I can't explain why right now.

rgds,
Roberto

* Emphasis added as the need to unfasten the batt terminals and pull fuses clearly seems to be a common misconception even amongst experts. No disrespect intended.

Its so inconvenient to lift up the long rear seat, put it somewhere out of the way, remove the terminal, put the DMM's leads on the terminal and battery securely, contort your body while doing this, wind down the window, run to the front, remove a fuse, run back and see if anything has changed, run to the front, replace the fuse, remove the next fuse, etc....and then fix the terminal back, and fix the seat back.....compared to simply bringing the DMM's leads to each fuse one after another, all in a row ? A 20 minute job turns into 5 minutes ?

Perhaps you're so used to this method that you don't notice the effort involved. I can certainly understand that....one's subjective perception of time varies according to one's competence and fluidity with any physical task.

Let me see if I can change your mind.

Sir, please do the same experiment that I did above with the trunk's fuse with the engine switched on and off with the trunk up, and then with the trunk down (engine on and off). In fact, please try it with the engine switched off, just the trunk up, then a read, then the trunk down, then another read. Of course, your trunk's light must be working.

Just try it once, with an open mind, and lets see if you don't get hooked right away. :-))

Because the meter won't be reading the full current present in the circuit. By measuring current in parallel, you are shunting some of the current across your meter, but not all of it. It defeats the purpose of the measurement.

When measuring current at low voltages, it is correct to always put the meter in series with the circuit being measured.

In this case, that means either pulling the neg (-) cable from the battery (to measure total current draw) or patching the meter in place of a fuse (to measure the current in a specific circuit).

Well OK, so I'll put the leads on the fuses to measure current draw when the car's key is out, and once I find something, I'll remove the fuse and jam in the leads instead to measure the actual current then.

Its still way easier than pulling the terminal and running back and forth, if all you're doing is wanting to trace a gremlin.

Besides, when you hook up an DMM set to the appropriate mA setting, you are introducing a near zero-resistance bypass into the system at the point of the fuse. The current will almost entirely pass through your ammeter instead of the two ends of the fuse, as current prefers a channel of lower resistance. You should be getting about a 99% accurate reading of the actual current flow in the live circuit, so even for academic purposes reading the current off the fuse would be correct.

Besides, when you hook up an DMM set to the appropriate mA setting, you are introducing a near zero-resistance bypass into the system at the point of the fuse. The current will almost entirely pass through your ammeter instead of the two ends of the fuse, as current prefers a channel of lower resistance. You should be getting about a 99% accurate reading of the actual current flow in the live circuit, so even for academic purposes reading the current off the fuse would be correct.

Are my assumptions correct here?

Not regarding the above statement. When electricity is involved, it's an especially bad idea to credit a presumption.

Not regarding the above statement. When electricity is involved, it's an especially bad idea to credit a presumption.

Its not quantum mechanics at the digital ammeter level and anyway thats why i asked you for confirmation.

Electricity flows from a point of higher voltage to a point of lower voltage. Electricity takes the path of least resistance. If there is more than one pathway between two points of potential difference, electricity flows by all the pathways but the bulk of the current (and sometimes overwhelmingly so) goes by the path of least resistance.

RB - You're punching above your weight. You remove the battery terminal and connect there so you can see when the current drops. If you prod about in the fuse box you COULD accidently hook accross a live pin load and then watch all the smoke come out of your ammeter set at 300ma. Pulling fuses out will not INCREASE the drain current - prodding the the fuse box - not a good idea.i

RB - You're punching above your weight. You remove the battery terminal and connect there so you can see when the current drops. If you prod about in the fuse box you COULD accidently hook accross a live pin load and then watch all the smoke come out of your ammeter set at 300ma. Pulling fuses out will not INCREASE the drain current - prodding the the fuse box - not a good idea.i

RB - You're punching above your weight. You remove the battery terminal and connect there so you can see when the current drops. If you prod about in the fuse box you COULD accidently hook accross a live pin load and then watch all the smoke come out of your ammeter set at 300ma. Pulling fuses out will not INCREASE the drain current - prodding the the fuse box - not a good idea.i

ok I have worked this out.

1. You would have to be negligent to hook across a live pin load that is large enough to fry your dmm but small enough not to do so if hooked in series with the battery. In fact, I can't really imagine how that would happen actually.

If you are worried about frying your dmm :

a. DMMs are fused, usually to 10A. They are fairly easy to dismantle and access the fuse if you need to replace it.

b. However, that is inconvenient and if you are still worried, then simply get a 5 or 7.5a car fuse, and tie it to one of your leads with pvc tape or even some gel or white silicone sealant, and use the other end of the car fuse as one lead while interrogating the fuses in the fuse box. Takes 3 minutes to set up. This fuse will burn way before the 10A internal fuse is triggered, and is much easier to replace.

c. When you connect your dmm to both ends of an installed car fuse, you are creating a circuit in parallel. Assuming that circuit is carrying current at the time, and depending on your ampere setting on your dmm, the internal resistance of the dmm changes accordingly, allowing very little current to flow through it anyway. So you can't burn out your dmm. The car fuse idea listed earlier is unnecessary, but its a painless precaution to take so why not.

In the interests of transparency, the bentley manual refers to the slow battery terminal method to identify current leaks.

Well Sir, as I said earlier, the Bentley manual agrees with your recommendation about the the battery terminal method that you've recommended. Here is the relevant extract, made possible due to the wonderful searchableness of searchable manual.

Because the meter won't be reading the full current present in the circuit. By measuring current in parallel, you are shunting some of the current across your meter, but not all of it. It defeats the purpose of the measurement.

When measuring current at low voltages, it is correct to always put the meter in series with the circuit being measured.

In this case, that means either pulling the neg (-) cable from the battery (to measure total current draw) or patching the meter in place of a fuse (to measure the current in a specific circuit).

You are correct Radian, except that this is not a test to measure current, but to see if there is any current flowing at all. Thus accurate ampere readings, nor connecting in series either through removed terminals or in place of removed fuses is not required.

7...8...9...OUT! Check current drain from the battery terminal to battery lead. Trust me on this RB, no point in telling fibs here.

Well I have done my checks, and here are the results.

1. Yes you can indeed use the ammeter's leads on BOTH ends of each fuse to determine if there is a current flow, with a low current draw setting which means high internal resistance selected on your multimeter ("mm"). If current registers on the display, you can then check if it makes sense eg clock circuit, or it doesn't eg luggage compartment light when the boot is closed, and take actions accordingly.

2. Why this method works perfectly is because you are placing your mm in parallel with each circuit. 3 aspects of electrical theory make this safe :

(a) The total current going into a junction of parallel circuits is the same as the total current coming out of it. I.e. the total current entering the junction splits up according to the various resistances in the parallel circuits and rejoins after passing through each line in the parallel circuit.
(b) If you place a high resistance device in parallel with a live circuit, though it offers an alternated pathway for current, it will draw very little current due to its high resistance, so you needn't be concerned
(c) The mm will not fry as well because the voltage in the car's circuit can never be higher than 12.6volts due to the battery's design and this is obviously safe for the mm.

Let me use a worked example that we can all relate to. The sparkplug. The actual spark itself is the current in the circuit. The potential difference between the plug's leads is the voltage. The spark will not kill us, its a ridiculously small current. However, the voltage of 20k-40k volts (I forget) will. So that's why its dangerous to humans. [ Always be mindful when around active ignition coils. As a rule, only work on and around it with the engine off and the ignition at key0. ]

On the car, the only device that can step up voltage like a transformer would be the ignition coils. And the voltage is stepped up solely within the coil itself and not in the external circuit that supplies it with the base current/standard voltage. So there is no risk that you will fry your mm if you test all of the car's circuits via the fuse box.

Thus, if you put your mm in series with the battery after disconnecting a terminal, you will destroy the mm's internal fuse (usually 10A) if the current draw somewhere else in the circuit happens to be higher than that. Put it in parallel.

Thus, the Bentley manual's method of searching for current draws is impractical to the point of being dumb when compared to the alternative. It involves waay too much work and time and risks your mm's fuse, as compared to simply connecting your mm's leads to both ends of each fuse in your fuse box, one after another. It just shows how powerful general superstitions can be that stuff like this makes it to the manual.

Remember, we are not trying to measure the current draw accurately. We are just trying to see if there is any current draw to begin with...when the engine is off with key0 on the ignition. So an accurate reading is not important.